1. Field of the Invention
The present invention relates to a position measuring apparatus adapted to detect a lateral variation of a stage during straight motion of the stage.
2. Related Art
A plurality of thin film magnetic heads are formed on a semiconductor wafer with the use of a thin film process, and thereafter the heads are cut off from the semiconductor wafer on which the magnetic heads are formed, for being separated from one another. Accordingly, if the accuracy of alignment of the heads formed in a row on the wafer is low, individual shapes and dimensions of magnetic poles become non-uniform (uneven) so that available characteristics of the magnetic heads are non-uniform. Thus, it is required to measure the alignment of an array of heads (which will be hereinbelow referred to xe2x80x9chead arrayxe2x80x9d) formed on the semiconductor wafer with a high degree of accuracy.
Heretofore, there has been used an apparatus for measuring an alignment of the above-mentioned head array, in which a semiconductor wafer is mounted and fixed on an X-stage guided by a direct-operated static air bearing, the direction of the head array to be measured on the semiconductor wafer being set to be coincident with the direction of movement of the X-stage, the wafer is moved by the X-stage, pitch by pitch for measurement while the alignment of the head array to be measured are measured by a TV microscope, in order to precisely measure an alignment of the array.
Although this apparatus can precisely measure the alignment of the head array on the basis of a degree of accuracy as to the straight guide of the direct-operated static air bearing, it can hardly avoid affection by vibration of air in the air bearing unit including a ball screw, a linear motor and the like for driving the X-stage, and accordingly, it is difficult to obtain a reproducibility of measurement within 0.02 xcexcm.
Further, there has been used another apparatus in which an X-Y stage 41 carrying thereon a wafer 46 is provided with an orthogonal plain reflector 42 in parallel with the X-axis and Y-axis, respectively, as shown in FIG. 5 of the accompanying drawings, illustrating an exposure apparatus used in the field of semiconductors, and displacements of the X-Y stage 41 in the X- and Y-axial directions are measured by laser interferometers 23, 24 for measuring relative displacements between themselves and the orthogonal plane reflectors 42.
However, in the above-mentioned conventional apparatus, although an alignment of a head array to be measured (that is, electronic devices formed on the wafer 46) is measured on the basis of the orthogonal plane reflector 42, it is required to position the X-Y stage 41 and the orthogonal plane reflector 42 over an entire measuring area in order to measure the alignment of the array over the entire measuring area on the wafer. Accordingly, the distances between the orthogonal plane reflector 42 and the laser interferometers 43, 44 should be set so as to include the above-mentioned entire measuring area in the extent of movement of the X-stage. For example, if the measuring area has 200 mm diameter, the distances between the orthogonal plane reflector 42 and the laser reflectors 43, 44 should be set to be greater than at least 200 mm diameter. In this configuration, if the temperature varies by 0.05 deg. C., thus measured distances vary by 200 mmxc3x970.5 deg. C.xc3x971xc3x9710xe2x88x926/deg. C.=1xc3x9710xe2x88x924 mm=0.1 xcexcm, and accordingly, it has been raised such a problem that this variation directly causes measuring errors.
Meanwhile, in order to measure an alignment of an array of electronic devices such as the above-mentioned thin film magnetic heads, the measuring errors should be settled within 0.01 xcexcm, and accordingly, a temperature difference should be held within 0.05 deg. C. during measurement. Further, in the above-mentioned conventional measuring apparatus, in addition to the temperature variation, a variation in the atmospheric pressure should be limited to a small value, and further, other mechanical deformation including thermal expansion should be limited to small values. However, it is difficult to economically materialize such an apparatus.
Further, in a process of manufacturing liquid crystal substrates or liquid crystal display elements, it is required to measures dimensions of a precise pattern such as a mask formed on the surface thereof. Heretofore, as to an apparatus for measuring such a precise pattern, there has, in general, been well-known such an apparatus that a substrate to be measured is shifted by an X-Y stage while an image of the precise pattern on the surface thereof is picked up by a TV microscope in order to measure the pattern.
By the way, these years, there has been raised such a demand that display units using the above-mentioned liquid crystal substrate or liquid crystal display elements, are required to be large-sized and highly accurate. In order to satisfy the above-mentioned demands even a two-dimensional liquid display apparatus for measuring dimensions of a precise pattern on the liquid crystal substrate or the liquid crystal display element, is required to high-precisely measure the precise pattern which is formed with a high degree of accuracy on such a large-sized substrate or element. Specifically, a reproducibility (measuring accuracy) of less than 0.1 xcexcm is required over a range of several hundreds to several thousands millimeters (several 100 to several 1,000 mm).
Conventionally, there has been used a two-dimensional measuring apparatus as shown in FIG. 6 of the accompanying drawings. That is, as shown in the figure, an X-stage 2 and a Y-stage 22 provided on a portal frame 21 extending across the X-stage 2 thereover are provided on a base 1, and a Z-stage 27 is assembled to the Y-stage 21 while a TV microscope 29 is mounted on the Z-stage 27. With this arrangement, the TV microscope 29 is positioned above the above-mentioned substrate while the X-stage 2, the Y-stage 22 and the Z-stage 27 are moved. It is noted that displacements of the X-stage 2 and the Y-stage 22 are precisely measured by means of laser interferometers 8a, 8b, 8c and plane reflectors 7a, 7b, 37. Thus, two-dimensional dimensions (in X- and Y-axial directions) of the point to be measured on the above-mentioned object to be measured can be obtained from the position of the point to be measured within the field of vision of the microscope, which is measured by the TV microscope 29 and the image processing device (which is not shown), and from the displacements of the X-stage 2 and the Y-stage 22 which are measured by the laser interferometers 8a, 8b, 8c. 
By the way, in the above-mentioned conventional two-dimensional measuring apparatus and the method therefor, reproducible measuring errors during measurement of, for example, dimensions, are added with errors caused by lateral motions of the stage during movement in X- and Y-axial directions. That is, when the stage is moved in, for example, the X-axial direction, lateral or sidewise motions are caused in the Y-axial direction (a direction orthogonal to the advancing direction of the stage) due to affection by yawing, rolling or the like during movement of the stage, and these lateral motions cause the errors. Thus, it is required to maximumly enhance the reproducibility of straightness during movement in X- and Y-axial directions, and accordingly, static air bearings 53a, 53b and 63 and linear drive motors 54, 64 are used in combination for guiding the stage in the X- and Y-axial directions.
However, with the above-mentioned technologies, since the accuracy of reproducible measurements falls in a range from about 0.1 to 0.2 xcexcm, the obtained straight guide reproducibility has become about 0.2 xcexcm. However, as mentioned above, since objects to be measured have become larger and larger, the static air bearings capable of moving the stage over a distance in a range from 100 to 1,000 mm require fabrication with a high degree of accuracy over its large dimensions, and accordingly, become extremely expensive. In addition, the linear drive motors are also expensive, and further, the heat value generated therefrom is high. Thus, excessive measuring errors due to thermal variations are caused in the apparatus which inevitably requires high measuring reproducibility and straight guide reproducibility, and accordingly, it has been unpreferable.
Further, in another two-dimensional measuring apparatus or method therefor, as shown in FIG. 7 of the accompanying drawings, a TV microscope 29 is positioned in the Z-axial direction, and then an X-Y stage 103 (which is not shown in FIG. 7), but which has a structure having an X-stage and a Y-stage superposed with the X-stage) is positioned in the X- and Y-axial directions. It is noted that the X-Y stage 102 is provided with plane reflectors 107a, 107b having reflection surfaces which are parallel with the X- and Y-axes, respectively, outside of an object to be measured, that is, at side surfaces thereof. Thus, displacements of the X-Y stage are measured also by laser interferometers 108a, 108b with a high degree of accuracy.
It is noted that, in this apparatus or method, the crossing point between laser beams emitted to the plane reflectors 107a, 107b from the laser interferometers 108a, 108b is set to be coincident with the optical axis of the TV microscope 29, and is set substantially at the same Z-axial position as that of the surface to be measured (that is, the top surface of the object to be measured). Thus, reproducible lateral motion errors can be measured, in principle, during straight movement in the X- and Y-axial directions by means of the laser interferometers. Specifically, if the X-Y stage 102 is moved in, for example, X-axial direction, a displacement of the plane reflector 107a in parallel with the X-axis is measured by the laser interferometer 108b, a lateral variation during straight motion on the X-axis (that is, a displacement in the Y-axial direction) can be measured.
By the way, with the above-mentioned conventional two-dimensional measuring apparatus or method, a lateral variation during straight motion of the stage with the use of the laser interferometers. However, the following problems have been raised.
That is, the Z-stage 109 is arranged across and over the X-Y positioning stage 102 which is moved in the X- and Y-axial directions, and further, the laser interferometers 108a, 108b are provided to end parts of the X-Y stage 102. With this configuration, the dimensions of a base 110 carrying them inevitably become larger. Accordingly, the gravitational load center of the base involving the weight of the X-Y stage is shifted as the X-Y stage 102 is moved, and accordingly, the base 110 is warped so that the distances and the positional relationship between the laser interferometers 108a, 108b and the plane reflectors 107a, 107b vary, thereby it has been raised such a problem that accurate measurements for displacements of the stage become difficult.
Further, in the above-mentioned configuration, since the distances between the laser interferometers 108a, 108b and the plane reflectors 107a, 107b become larger than the dimensions (for example, several 100 to several 1,000 mm) of an object to be measured, the measurements for displacements of the stages are susceptible to affection by environment including a temperature and an atmospheric pressure, and accordingly, there has been also raised such a problem that measuring errors becomes excessive. That is, if a plane reflector and a laser interferometer are arranged so as to set the distance therebetween to, for example, about 200 mm, when the temperature varies by 0.5 deg. C. so that the refractive index of the air is changed, the measuring distance varies by 200 mmxc3x970.5 deg. C.xc3x9710xe2x88x926/deg. C.=1xc3x9710xe2x88x924 mm=0.1 xcexcm, and accordingly, it has been raised such a problem that this variation also directly causes measuring errors. Accordingly, the above-mentioned configuration can not always exhibit satisfactory reproducible measuring errors or real guide reproducibility.
That is, as mentioned above, since the dimensions of objects to be measured become greater and greater or the precision of patterns become higher and higher, although measuring reproducibility less than 0.1 xcexcm can be obtained over a range from several 100 to several 1,000 mm, real reproducible lateral motion errors during straight movements of the X-Y stage in the X- and Y-axial directions directly cause measuring errors in the conventional technology. Moreover, since heat generated from the stage drive system becomes higher, the above-mentioned configuration is inappropriate for the above-mentioned highly accurate measuring, and is extremely expensive.
The present invention is devised in view of the above-mentioned problems inherent to the prior art, and accordingly, a first object of the present invention is to provide a two-dimensional measuring apparatus which can economically exhibit reproducibility of measuring an alignment of an array with accuracy of about 0.01 xcexcm.
Further, a second object of the present invention is to provide a two-dimensional measuring apparatus which can greatly reduce measured reproducible lateral errors during straight movement of an X-Y stage so as to obtain sufficient measuring reproducibility with no use of an expensive drive and guide system, and which is inexpensive, even though the apparatus is large-sized.
To the end, according to a first aspect of the present invention, there is provided a position measuring apparatus for detecting a lateral variation during straight motion of a stage, comprising:
a base;
an object holding unit for holding thereon said object to be measured;
a first stage, on which the object holding unit is placed;
a first axial drive and guide unit for driving and guiding the first stage in a first axial direction;
an image detecting unit provided above the object holding unit, for picking up an image of the object so as to deliver an image signal thereof;
a first detection unit for detecting a lateral variation during straight motion of the first stage in the axial direction, the first detection unit provided in the vicinity of the side surface of the first axial direction of the objet holding unit; and
a compensating unit coupled with the first detection unit, for compensating the image signal outputted from the image detection unit on the basis of a signal from the first detection unit.
Further, in a specific form of the first aspect of the present invention, the position measuring apparatus further comprises a second stage provided on the base, across and over the first stage, and adapted to move in a direction orthogonal to a moving direction of the first stage, and the image detecting unit being provided above the second stage.
Further, in a further specific form of the first aspect of the present invention, in the position measuring apparatus first detection unit comprises a plane reflector attached to a first axial side surface of said object holding unit, for reflecting laser light and a laser interferometer provided in the vicinity of and in opposite to said plane reflector.
In addition, in another specific form of the first aspect of the present invention, in the position measuring apparatus, a distance between the laser interferometer and the plane reflector is shorter than the maximum moving distance of the first stage in the first axial direction.
In a further specific form of the first aspect of the present invention, in the position measuring, the distance between the laser interferometer and the plane reflector is set to a value within a range of several mm.
In a further specific form of the first aspect of the present invention, a position measuring further comprises a rotation table provided between said first stage and said object holding unit, for rotating said object to be measured.
In a further specific form of the first aspect of the present invention, in a position measuring apparatus, the first axial drive and guide unit comprises either one of a ball screw and a linear motor.
According to a second aspect of the present invention, there is provided a position measuring apparatus for detecting a lateral variation during straight motion of a stage, comprising;
a base;
an object holding unit for holding thereon an object to be measured;
a first stage, on which the object holding unit is placed, provided above the base, for moving the object holding unit in a first axial direction.
a sub-base arranged on the base and extended in a second axial direction orthogonal to the first axial direction;
a second stage adapted to move on the sub-base in the second direction;
a first and a second axial drive and guide unit for driving and guiding the first and second stages in a first and second axial direction, respectively;
an image detecting unit provided on the second stage, movable in a third axial direction orthogonal to the first stage, for picking up an image of the object to be measured so as to deliver an image signal thereof;
a first detection unit provided in the vicinity of a side surface of the first stage which extends in the first axial direction, for detecting a lateral variation during straight motion of the first stage in the first axial direction;
a second detection unit provided in the vicinity of a side surface of the second-stage which extends in the second axial direction, for detecting a lateral variation during straight motion of the second stage; and
a compensating unit coupled with the first and second detection units, for compensating the image signal outputted from the image detection unit on the basis of signals outputted from the first and second detection units.
In a specific form of the second aspect of the present invention, in the position measuring apparatus, a first distance between the first detection unit and the side surface of the first stage which extends in the first axial direction, and a second distance between the second detection unit and the side surface of the first detection unit which extends in the second axial direction are shorter than maximum moving distances of the first and second stages in the first and second axial directions, respectively.
In a further specific form of the second aspect of the present invention, in the position measuring apparatus, the distance between the first detection unit and the side surface of the first stage which extends in the first axial direction and the distance between the second detection unit and the side surface of the first detection unit which extends in the second direction are set to be within a range of several mm.
In a further specific form of the second aspect of the present invention, in the position measuring apparatus, each of the fist and second axial drive and guide units, comprises a motor and a ball circulation type linear guide.
In a further specific form of the second aspect of the present invention, in the position measuring apparatus, each of the first and second detection units comprises either one of a triangulation type laser displacement meter or a laser interferometer.
In a further specific form of the second aspect of the present invention, in a position measuring apparatus, the first and second stages are moved respectively in the first and second axial directions in a range of several 100 mm to 1,000 mm.
The present invention will be detailed in the form of preferred embodiments with reference to the accompanying drawings.